Antenna structure



L. ESPENSCHIED. ANTENNA STRUCTURE.

APPLICATION FILED SEPT.26, 1919.

Patented Sept. 21, 1920.

INVENTOR.

Llgyd d rromvzy,

UNITED STATES PATENT OFFICE;

AMERICAN TELEPHONE NEW YORK.

ANTENNA STRUCTURE.

Specification of Letters Patent.

Application filed September 26, 1919. Serial No. 326,524.

T 0 all whom it may concern Be it known that I, LLOYD ESPENSOHIED, residing at Hollis, in the county of Queens and State of New York, have invented certain Improvements in Antenna Structures, of which the following is a specification.

This invention relates to radio transmission and more particularly to antenna arrangements for radio systems.

One of the principal features of the invention resides in the provision of an an-- tenna arrangement having the characteristics of a broad band filter, that is a filter which will freely transmit a wide band of frequencies with uniform attenuation, while substantially extinguishing frequencies 1ying without the band.

A further feature of the invention resides in the provision of a terminating impedance associated with the end section of a series of sections of an antenna having a broad band characteristic, said impedance being for the purpose of substantially preventing reflection losses due to the fact that the number of sections is less than infinite.

These features, together with other fea tures of the invention more fully appearing hereinafter, are realized in an antenna structure made up of a plurality of similar sections, each section comprising a series impedance element which is preferably an in-' ductance and capacity in series with each other and a shunt impedance element connected to ground and constituting with the normal capacity to ground of the section, a shunt element comprising parallel inductance and capacity.

In accordance with the principles set forth in the United States Patents, Nos. 1,227,113 and 1,227,114, issued to George A. Campbell, under date of May 22, 1917, such a structure when composed of an infinite.num-- ber of sections may, by proper design of the elements constituting each section, freely transmit a band of frequencies with uniform attenuation, while substantially suppressing frequencies lying without the band. Sincein practice it is not feasible to provide an infinite number of filter sections, a lesser number may be used with substantially the same result, provided the end sections of the series are related to terminal lines or other elements having the proper impedance values. In the construction of an antenna, however, since the aerial member of an antenna is open-circuited at one end, the last section of an antenna structure, such as above described, would not be connected with a proper impedance, so that reflection losses would result. It is therefore proposed to associate with the last section of the series a terminal impedance element so related to a small number of sections that the effect of reflection losses will be substantially eliminated. i

The invention may now be more fully understood from the following description when read in connection with the accompanying drawing, the figure of which illustrates the general embodiment of the invention.

Referring to the drawing, A designates generally an antenna arrangement comprising a plurality of sections of similar construction. Each section comprises series in ductances Ls and series capacities C in series with each other and a shunt inductance L connected to ground. The normal capacity of the section to ground may be con sidered to be in parallel with the inductance L as indicated in dotted lines. It will thus be seen that the antenna arrangement con- Patented Sept. 21, 1920.

stitutes one of the types of band filters disacteristic. Accordingly, the right hand section has associated therewith an impedance element X,-which comprises a resistance 1 and a capacity 2, so proportioned as to give the proper terminating im edance. In actual practice the capacity 5 and the capacity 2 may be combined in one condenser, but are separately illustrated, in order that the'relation of the parts may be more clear. The left hand section of this series should also be provided with a similar terminating impedance and for this purpose a capacity 2 is provided, the resistance corresponding to the resistance 1 being taken as the resistance of the transformer 3 and other apparatus whereby the multiplex circuits may be associated with the antenna. a

The multiplex circuits are associated with the antenna through a common transmitting circuit TL and a common receiving circuit -RL. The latter is connected to the secondary winding of the balanced transformer 3. The circuit TL has one conductor grounded, while the other conductor is connected to the midpoint of the split winding of the transformer 3. In order that the circuits TL and RL may be rendered substantially conjugate, an artificial line or network AN is provided to balance the antenna structure A over the range of frequencies to be transmitted.

L and L designate a plurality of low frequency signaling lines adapted to transmit signals through the medium of the antenna structure A. The line L is associated with the circuits TL and RL through transmitting channel TL and receiving channel lRL respectively. The line L is similarl associated with the circuit TL and B through the channels TL and R11 respectively. The transmitting channel TL includes a modulator M a band filter TF an amplifier TA and a band filter TF The modulator M, is of any well-known character but is preferably a vacuum tube modulator such as is disclosed in the U. S. application of John R. Carson, Serial No. 157,413, tor is adapted to modulate a radio frequency f applied thereto in accordance with signals incoming from the line L.

The filters TF v and TF, are preferably band filters of the type illustrated in the patents to Campbell above referred to. The filter TFv is designed in accordance with the principles of said Campbell patents, to transmit a band of frequencies above a desired lower limit, while suppressing frequencies below this limit and also to suppress frequencies above a desired upper limit. The lower limit of the filter should be so chosen as to pass the modulated carrier frequencies, while suppressing low frequency components, while the upper limit should be so chosen as to suppress harmonics of the carrier frequency. The filter TF is designed to transmit a relatively narrow band of frequencies in the neighborhood of the frequency f the band being sufliciently wide, however, to accommodate the frequencyvariation due to the modulation of the frequency f, by the signaling currents. This function may be performed by filter TF and the filter TF used merely to selectively. combine the outputs from circuits TL and TL, The amplifier TA which is included in filed March 26,1917. This modula-.

- frequencies the channel TL, between the two filters, may be of-"any well-known type. It is, however, preferably a vacuum tube amplifier 'of the well-known push and pull type, since this type of amplifier tends to distort high frequencies to a lesser extent than the ordinary vacuum tube amplifier.

The receiving channel RL includes a lfi nd filter RF a demodulator or detector 1 The band filter RF is of thegeneral type disclosed in the patents to Campbell, above referred to, and is sodesigned as to transmit a band of frequencies in the neighborhood of the basic frequency assigned to this receiving channel. Where transmission and reception take place at the same frequency, the filter RF, may therefore be identical in construction with the filter TF In radio systems, however, it is desirable that reception take place at a different frequency from transmission, in order to suppress the transmitted energy absorbed by the receiving circuit, due to unbalance. If therefore the basic carrier frequency assigned to the channel RL be 71, the filter RF, should pass a band of frequencies in the neighborhood of the frequency f,, sufiiciently wide to accommodate the frequency variation due to modulation.

The detector D may be any well-known type of detector, but is preferably a duplex vacuum tube detector of the type illustrated in the U. S. application of'John R. Carson, Serial No. 157 ,414, ,filed March 26, 1917. This type of detector operates upon the socalled homodyne principle of reception and is therefore supplied with oscillations of carrier frequency f,, which react with the received modulated carrier frequency to produce in the output of the detector the low frequency currents in accordance with which the carrier frequency was modulated at the distant transmitting station.

The amplifier RA, may be of any desired type, but is preferably an ordinary vacuum tube amplifier adapted to amplify low frequency currents The filter RF, is arranged in the output circuit of the amplifier and isso designed as to suppress high frequencycomponents while freely transmitting the detected low frequency currents.

The transmitting channelTL associated with the line L includes a modulator M filter TF amplifier TA and filter TF all of these pieces of apparatus being in general similar to those described in connection with the line TL The modulator M is supplied with a carrier frequency f however, instead 'of f in order that the proper frequency separation between the channels be maintained. The filter TF will therefore be accordingly designed to transmit a band of of substantially the same Width as that transmitted by the filter TF ,'but

said band in this instance will lie in the neighborhood of the frequency 7",, instead of the frequency f The receiving channel RL, likewise includes a filter RF a detector D an amplifier RA and a filter R1 The detector D is supplied with homodyne currents having a frequency f corresponding to the carrier frequency assigned to the channel. The filter RF is accordingly designed to transmit a band of frequencies in the neighborhood of the frequency f The several pieces of apparatus are otherwise similar to those described in connection with the channel RL The operation is as follows: Low freiuency signals incoming from lines L and 2 are impressed upon the modulators M and M to modulate the carrier frequencies f, and f in a well-known manner. The modulated currents are then passed through the filters TF and TF amplified by the amplifiers TA and TA and then passed through the filter TF, and T F to the common transmitting circuit TL. The several modulated carrier frequencies are now impressed upon the midpoint of the antenna winding of the transformer 3, so that part of the energy passes through the balancing network A to ground and part of the energy is transmitted to the network comprising the antenna A, for radiation to a distant receiving station. Owing to the broad band characteristic of the antenna structure A, the several modulated carrier frequencies will be radiated with-substantially the same amplitude, the terminal network X and its electrical equivalent, the condenser 2' and the transformer 3 functioning to prevent reflection effects which might otherwise disturb the filtering action of the antenna structure.

Since the energy transmitted from the circuit TL flows in opposite directions through the two halves of the primary wind ng of the transformer 3, only a small amount of energy due to unbalance will be impressed upon the circuit RL and this energy will be suppressed by the filters RF and RF since the frequencies of the transmitted energy are different from the frequencies used in reception.

A plurality of modulated radio frequencies received from, a distant sending station are absorbed by the antenna A and due to its broad band characteristics, these frequencies are impressed through the transformer 3 upon the common receiving circuit RL, with substantially equal amplitude. The several frequencies are now selected into the proper receiving channels RL and RL by means of the filters RF, and RF and the low frequency currents in accordance with which the radio frequencies were modulated at the distant station are detected by means of the detectors D and D The low frequency currents are then amplified by the amplifiers circuits TL and RL.

It will also be obvious that the general principles herein disclosed may be embodied in many other organizations widely different from those illustrated, without departing from the spirit of the invention as defined in the following claims.

What is claimed is:

1. An antenfna structure for multiplex transmission comprising a plurality of sections, each section including a series impedance element and a shunt impedance element connected to ground, and a terminating impedance associated with the end section of the series, the impedance elements of each section being so proportioned and related to each other that the combination will freely transmit with substantially equal attenuation a broad band of frequencies, while substantially suppressing frequencies lying outside the band, and said terminating impedance being so proportioned as to substantially prevent reflectionv losses due to the fact that the number of sections is not infinite.

2. An antenna arrangement for multiplex radio transmission, comprising a plurality of sections, each section including an inductanceand capacity in series and a shunt inductance connected to ground, and a terminal impedance element associated. with the end section of the series, the elements of each section being so proportioned and related to each other than the combination will freely transmit with uniform attenuation a band of frequencies, while substantially extinguishing frequencies lying without said band and said terminal impedance being so proportioned as to substantially prevent reflection losses due tothe fact that the number of sections in the series is not infinite.

3. An antenna structure for a multiplex radio system, comprising a plurality of sections, each section including an inductance and capacity in series and a shunt inductance connected to ground and comprising with the normal capacity to ground of the section, a parallel combination of inductance and capacity, and a terminal impedance element associated with the last section of the series, the inductance and capacity elements of each section being so proportioned and related to each other and to the normal capacity to ground of the section that the combination of sections will freely transmit with uniform attenuation a band of frequencies while substantially suppressing frequencies lying without the band, and said terminal impedance element being so proportioned as to substantially prevent reflection effects due to the fact that the number of sections is less than infinite.

4:. An antenna structure for radio transmission comprising a plurality of sections, each section including a series impedance element, the impedance elements of each.

section being so proportioned and related to each other and to the antenna capacity of each section that the combination will freely transmit with substantially equal attenuation a broad band of frequencies, while substantially suppressing frequencies lying outside the band.

In testimony whereof I have signed my name to this specification this 25th day of 20 September,

, LLUYD ESPENSCHIED 

